1. Field of the Invention
The present invention relates to a positive resist composition suitably used in the ultramicrolithography process of producing, for example, VLSI or high-capacity microchip or in other photofabrication processes, and a pattern formation method using the composition. More specifically, the present invention relates to a positive resist composition which can be suitably used for forming a highly refined pattern with use of an electron beam, EUV light or an X ray, and a pattern formation method using the composition.
2. Description of the Related Art
In the process of producing a semiconductor device such as IC and LSI, fine processing by lithography using a resist composition has been performed. Recently, the integration degree of integrated circuits is increasing and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using an electron beam, an X ray or EUV light is proceeding.
The electron beam lithography using a positive resist is positioned as a pattern formation technique of the next generation or second next generation and this is a promising technique for the formation of an ultrafine pattern of 150 nm or less but in addition to high sensitivity and high resolution, more improvements are demanded on the pattern profile, line edge roughness, dissolution contrast, inhibition of negative conversion, and surface roughness.
The lithography using an X ray or EUV light also has the same problems and it is necessary to solve these problems.
In the lithography process using an electron beam, an X ray or EUV light, a chemical amplification-type resist utilizing an acid catalytic reaction is mainly used in view of high sensitivity. As for the positive resist, studies are being made on a chemical amplification-type resist composition mainly comprising an acid generator and a resin which is insoluble or sparingly soluble in an alkaline developer but of which solubility in an alkaline developer increases by the action of an acid.
Examples of the positive resist composition include those described in JP-A-2004-4227 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)), JP-A-2003-40840, JP-A-2003-140361 and JP-A-2003-140342.
However, the lithography process in the ultrafine region at present fails in satisfying good pattern profile, line edge roughness, dissolution contrast, surface roughness and prevention of negative conversion, as well as high sensitivity and high resolution.